"The Supreme Court's decision raises the possibility of a significant increase in the number of inquiries, referrals and status verification inquiries from Arizona state authorities that will impact DHS's immigration enforcement operations," the department said Monday in a note to field offices.
Arpaio, the controversial Phoenix lawman known for his anti-immigration raids, said he was concerned whether federal agents will decline to pick up some illegal immigrants who are stopped by his deputies.
"I have my suspicions," he said.
Arpaio asked a federal judge earlier this month to dismiss a lawsuit that claims his office discriminated against Latinos in the sheriff's trademark immigration patrols and had a culture of disregard for basic constitutional rights.
Hours after Monday's ruling, the Department of Homeland Security canceled agreements with seven Arizona police departments that deputized officers to arrest people on immigration violations while on street patrol.
Phoenix Police Chief Daniel Garcia declined to detail how the statute will play out but anticipates it won't be much of a departure from what officers already do.
"It's much too early to try to speculate on these issues of law," he said.
If federal agents decline to pick up immigrants, the state doesn't have any way to force federal authorities to pick them up and will likely have to let them go unless they're suspected of committing a crime that would require them to be brought to jail, said Peter Spiro, a Temple University law professor who specializes in immigration law.
In that sense, the law is symbolic, Spiro said. The questioning requirement "is useful to the extent that it allows states to give notice of hostilities to undocumented immigrants," Spiro said. "It allows for a formal expression of the state's hostilities toward undocumented immigrants."
Arizona Gov. Jan Brewer called the decision a victory for all Americans, but said she expected lawsuits to challenge the implementation of the law.
"It's certainly not the end of our journey," she said.
Responding to criticism that the law would lead to racial profiling, Brewer said that any officer who violates a person's civil rights will be held accountable. Even while upholding the provision, the justices said the status check could be challenged.
Homeland Security Secretary Janet Napolitano said in a written statement that the Supreme Court's ruling will make her agency's work more challenging, but she was pleased that the court ruled state laws can't dictate the federal government's immigration enforcement priorities.
Immigration rights groups said they were surprised and disappointed by the court's decision, and planned to ask the lower courts to block the law.
"The opinion invites the challenges that we are bringing. It's going to cause racial profiling. It will cause prolonged detentions," said Linton Joaquin of the National Immigration Law Center, one of the groups pushing a separate challenge to the law.
Arizona passed the law in 2010, with lawmakers arguing that that federal government wasn't adequately preventing illegal immigration. The Obama administration sued to block it, saying that enforcing immigration laws was a federal responsibility.
Associated Press writers Jacques Billeaud, Terry Tang and Felicia Fonseca in Phoenix contributed to this report.
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